1. Field of the Invention
The present invention relates to a motorcycle. In particular, the present invention relates to an air intake structure for an air filter included in a motorcycle engine.
2. Description of the Related Art
The engine of a motorcycle is the source of its power. An engine needs air to carry out combustion. Therefore, the engine of a motorcycle is configured upstream with a fuel injection device or a carburetor for providing the mixture of air and fuel that the engine needs to carry out combustion within the cylinders. The fuel injection device or carburetor must provide the engine with appropriate mixtures at appropriate times given various engine environments and factors such as idling, low speed, and high speed. However, the air in the external environment in which motorcycles are operated usually carries a lot of muddy water or dust. If these impurities are sucked into the engine, they might result in poor engine combustion efficiency and may even damage the engine. Therefore, to solve this problem, an air filter is always installed in the air intake structure of the motorcycle engine in order first to filter out the various impurities described above from the air. Only then is the filtered air, passing through manifold inlets, introduced through the fuel injection device or carburetor into the engine so that it can undergo combustion.
All air filters have an air inlet for introducing external air into the air filter. FIG. 7 shows a diagram of the air intake structure of a conventional motorcycle air filter 131. The air filter 131 is disposed above the motorcycle engine. As shown in FIG. 7, in a conventional engine intake structure, the air inlet 132 is formed with an opening which is in the front end of the main body of the air filter 131 and which is oriented directly toward the front of the vehicle. Therefore, the air inlet 132 easily sucks in muddy water or dust from the front while the motorcycle is being operated. In addition, because the air inlet 132 is relatively close to the ground and is installed near the rear wheel of the vehicle, muddy water, dust, or other such impurities that are splashed up from the ground during vehicle operation are extremely likely to be drawn into the air filter together with the air. In particular, muddy water, etc. is easily splashed through the air inlet into the air filter when the vehicle travels down a stretch of road that is full of puddles. The problem has been solved in conventional engine air intake structures by adding a shielding portion 133 located above, below, or around the air inlet to prevent various impurities from infiltrating the interior of the air filter 131 through the air inlet. However, in such a structure, it is necessary to add the shielding portion 133 at the air inlet 132. Since the air filter 131 is installed low on the frame of the rear half of the vehicle body, where there are elements such as the motorcycle's vehicle body frame, the engine unit including the crankcase and the transmission case, ducts, and the rear mud flap, the space available for installation is extremely limited in this area. Thus, the addition of the shielding portion 133 at the air inlet 132 of a conventional air filter 131 results in the occupation of more space, with the result that the motorcycle's design becomes complex, which, in turn, leads to increases in the size of the vehicle body. In addition, because this area is near the rear wheel of the motorcycle, the muddy water, dust or other impurities that are sprayed up by the rear wheel when the motorcycle is traveling at high speeds will still easily avoid the shielding portion 133 and enter the air filter through the air inlet. As a result, the air filter 131 still might suck in impurities.
In addressing this type of problem, the conventional art has structures wherein a shielding portion is not used at the air inlet. Please refer to FIG. 8. FIG. 8 is a diagram that shows another air intake structure of a conventional motorcycle air filter. As shown in FIG. 8, the conventional air intake structure entails installing the air filter 100 behind the storage box 104 above the motorcycle engine and mounting the air filter 100 with fasteners such as bolts, or welding it, on the left-side and right-side vehicle frames 101 and the transverse tube 102. Then, above the transverse tube 102, an air inlet 103 oriented toward the rear of the vehicle is installed on top of the air filter 100.
However, in the air intake structure of the conventional engine air filter arranged as shown in FIG. 8, the air inlet 103 opens toward the rear of the vehicle and is installed near the rear wheel. Therefore, when the vehicle is traveling forward at high speeds, impurities such as muddy water or dust which are carried by the upper portion of the rear side of the rear wheel are sprayed forward and upward by the rapid rotation of the rear wheel. As a result, the concern remains that the air inlet 103 may suck in a considerable amount of impurities. In addition, since the air filter 100 is installed behind the motorcycle's storage compartment 104, the storage compartment 104 is compressed, with the result that the storage compartment 104 has less space available for storage.
Both the motorcycle industry and riders long for effective improvements and solutions to the various problems with the air intake structure of the conventional motorcycle engine air filters described above in order that the aforementioned problems with impurities easily entering the air filter and thus affecting vehicle engine performance may be solved.
However, the internal vehicular space of a motorcycle is itself already very limited and, given the trend toward reduced weight and size, the space available for installing a shielding portion that will effectively prevent impurities from entering the air filter from the air filter's air inlet is even more limited. Therefore, to maintain long-lasting, superior engine performance, the installation of a good air intake structure on a motorcycle requires two things: first, that no more of the limited internal space of the motorcycle be used up; second, that impurities can be truly and effectively prevented from entering the air filter through the air inlet of the air filter. This is absolutely not a simple matter. Therefore, in the quest to fully satisfy both requirements, designers and manufacturers in the industry have long had difficulty in developing and commercializing an effective solution.